Following are some acronyms used in this description:                LTE long term evolution        UTRAN UMTS terrestrial radio access network (3G)        E-UTRAN evolved UTRAN (3.9G or LTE)        UE user equipment        LA location area        TA tracking area (similar to LA)        LAU LA update        TAU TA update        eNB evolved NodeB (base station or access node of LTE)        BCH broadcast channel        GSM global system for mobile communications        CDMA code division multiple access        PLMN public land mobile network        WLAN wireless local area network        GERAN GSM EDGE radio access network        
Mobile user equipment transits through various geographic areas and in the process moves from control of one network cell to another to maintain its wireless link with a core network through which data and calls are routed to and from other entities. Generally, the UE will check for neighboring cells at certain specified times when the host cell knows not to page the UE (e.g., idle mode), request a handover to a particular neighbor cell when the UE deems it appropriate, and execute handover procedures as directed by the network. Even where different network operators controlled the different cells, generally in traditional systems any neighbor cell that gave an acceptable signal to the UE was considered a candidate for a handover. Exceptions existed and still exist when a particular cell was incompatible, from a technology standpoint (e.g., GSM versus CDMA) with the UE's capabilities, but since the UE was incompatible with the protocol used by those other cells, the UE never considered them as candidates for a handover.
Several network layers/networks/technologies may co-exist in the same coverage area. Some subscribers/user equipment may have access rights to several of these in a same geographical position. Network operators seek to cover new market segments, and 3G mobility procedures favor large cell sizes (e.g. large as compared to WLAN). In current cellular systems the mobility management is mostly coverage based, even with hierarchical cell structures. Generally, seamless mobility for the UEs is enabled by neighbor cell information provided by the serving cell. Several network operators have expressed an interest in creating wireless network layers with restricted access, e.g. company networks, home basestations etc. A recent technical report (TR R3.018 V0.1.0 (2006-01)) from the radio access network working group WG RAN3 assigns the subscription information handling functionality in the eNodeB, following the trend to translate traditional core network functions into the radio network. As these private networks become more common, a problem arises in that any particular UE must distinguish between those cells to which it can be handed over and those cells to which its access is restricted.
Under the coverage-based approach of traditional idle mode, the operators cannot control the accessibility of the UE subscriber to parts of their network in an efficient way due to other reasons, e.g., based on subscription class. Subscription based mobility control could be handled in theory at the core network (e.g., via Location Areas LA), but this approach causes unnecessary signaling and results in higher network maintenance. Roaming is not an efficient option for this because roaming is based on PLMN codes, which have only a few bits and is seen to exhibit difficulty in implementation (e.g. roaming contracts).
WLAN systems are not seen to use neighbor cell information, one just installs the access point and sets the carrier frequency. With small cell sizes (Pico cells, Femto cells) the construction of the neighbor cell relationships is a tedious task. Even if the neighbor cells would be known, in 3G the maximum number of inter-frequency neighbors is 32. If mobility between a macro cell and more than 32 other cells is desired, say Femto cells, merely extending the prior art 3G mobility concepts tend to indicate that aggressive scrambling code reuse would need to be employed.
In the E-UTRAN one of the requirements is to support e.g. home eNB's. This highlights a problem also relevant in legacy systems (GSM and UTRAN) concerning efficiently restricting some UE's access to certain cells using a minimum amount of signaling while still providing efficient functionality both from the UE and the network point of view. In LTE an identified problem has been how the UE is supposed to identify which cells allow access by the UE and which cells do not, e.g. private network/home base stations may restrict access to certain UEs only. Another problem is how to ensure that UEs with no access permission to one or more particular cells will not consider these cells as viable candidates for cell selection/reselection by that UE.
There have been considerations to use a forbidden location area concept for these purposes. A problem arises when there are large numbers (e.g., hundreds) of private networks and the UE tries to access each of those private networks before it receives an indication that the particular TA is forbidden (either through reading of TA code or TA update). Using the approach that the UE must first attempt access to each network/cell prior to placing that network/cell in its forbidden list poses several problems to both the network and the UE. Specifically:                Signaling is needed and increased for each private network or Home-eNB.        UE power consumption due to this signaling is increased.        The time when the UE is not reachable for paging might increase.        UE memory consumption: as time passes the number of forbidden TAs may rise to a significant number. UE would either need to remember the whole list of TA's which are forbidden or alternatively the UE may have to restrict the list to a maximum number (which then may increase signaling further).        
Legacy systems such as interworking scenarios between 2G and 3G wireless systems attempt to handle these types of access restrictions by the use of location area, location update procedure and even the use of specific causes for location update rejections.
The inventors have disclosed one approach for generating and using forbidden neighbor lists for distinguishing allowed from restricted cells in PCT/IB2007/004139, referenced above. That disclosure is seen as most advantageous for environments where the amount of cells under consideration is not large. However, further adaptation is preferable to handle a large amount of private cells (e.g. Home-eNB's) without significantly expanding the signaling required so that a UE can distinguish between allowed and restricted cells.
A particular cell or network may be allowed or restricted for any of various reasons. Most applicable to these teachings is the case where the cell restricting access by a particular UE is fully operational, but does not allow access to that UE, such as private networks and home eNBs. It is in those environments where the number of cells that restrict the UE's access are most likely to accumulate to a larger number, though the teachings herein are not limited by any particular reason a cell is deemed as restricted or allowed for a particular UE. Certain cells restricting UE access may be due to temporary measures imposed by the network such as maintenance, and any cell may be identified to the UE in the same manner, according to the specific teachings below, to indicate whether it is allowed or restricted for the UE.